Your question has a very simple answer. Remember first that the NTSB is NOT a regulatory agency but a government approved investigative body without regulatory authority. They can only publish findings and make recommendations. It is the Department of Transportation, Federal Aviation Administration that enforces Codes of Federal Regulations in a court of law.
FAA investigates incidents and accidents and proposes sanctions if non compliance is found. The result of an accident can be a fine levied against an operator (airline) or suspension or revocation of a pilot's certificate.
As long as we have men and women flying aircraft the potential for accidents is always there. We have made amazing progress in the areas of safety but the threat or inevitability for an accident will always be there.